This invention relates to an improved magnetic tape head and its method of manufacture.
Magnetic tape heads typically have raised strips or ridges, commonly referred to as islands, that provide raised tape support or wear surfaces with embedded transducers across which magnetic tape advances. These embedded transducers can be either a recording element for writing information onto a magnetic tape or can be a reproducing element for reading information off a magnetic tape. An embedded recording element produces a magnetic field in the vicinity of a small gap in the core of the element, which causes information to be stored on magnetic tape as it moves across the support surface. In contrast, a reproducing element detects a magnetic field from the surface of magnetic tape as the tape moves over the support surface.
Normally there is some microscopic separation between the transducer and magnetic tape during operation that reduces the strength of the magnetic field coupled to the tape surface during the recording process. During the reproducing process, the separation reduces the coupling between the tape field and the reproducing element. This reduction in magnetic field strength is know as "spacing loss".
Magnetic field strength detected by a tape or by a reproducing element is proportional to e .sup.-kd/.lambda., where d is the head-to-tape separation, .lambda. is the recording wavelength, and k is a constant. As is apparent, detected magnetic field strength decreases exponentially both with respect to separation between the tape and the raised support surface of an island and with respect to recording density (which is inversely related to the recording wavelength). Thus, while a limited amount of head-to-tape separation might be acceptable at low recording densities (10-20 KFCI), smaller transducers used with magnetic tapes of higher recording densities (40-80 KFCI) can tolerate substantially no head-to-tape separation. Accordingly, there is an important need for coordinated wear between raised support surfaces and transducer surface regions of magnetic tape heads to keep head-to-tape separation within acceptable tolerances.
When uniform tension is applied to a recording tape as the tape passes at a wrap angle on the raised support surface of an island having a uniform height and a uniform width, the tape exerts a pressure against the raised support surface of the island that is uniform along the longitudinal axis of the island. And this uniform pressure is essentially proportional to the tension and the wrap angle and inversely proportional to the island width.
Tape pressure against the raised support surface of an island can be modified. For example, the pressure can be changed by modifying the tension in the tape, by modifying the wrap angle of the tape on the support surface of the island, or by modifying the width of the raised support surface of the island. Accordingly, pressure on the surface of an island can be increased by increasing the tension in the tape, by increasing the wrap angle of the tape on the support surface of the island, or by decreasing the width of the support surface. In this regard, increased pressure reduces "spacing loss".
But increased pressure has negative consequences. For example, increased pressure reduces tape life and increases the possibility of tape damage and data loss. Also, increased pressure causes islands to wear down more quickly. And this accelerated island wear results in shortened head life. Moreover, increased pressure can result in uneven wear along raised support surfaces. Uneven wear can be particularly bothersome between regions of an island with a transducer and regions of an island without a transducer. This uneven wear can also result in shortened head life and can contribute to "spacing loss".
In practice, tape support islands and cores can be made of a variety of materials, each with own manufacturing advantages. However, the best wear matching is achieved when they are made from the same material, hence the manufacturing advantage such as lower cost, are lost. The problem of using various material is during normal operation and under the same pressure, these various materials wear at different rates. In order to use different material, a very difficult and time consuming method is required in order to select compatible material. Hence, only a limited number of composite structures are used and often results in uneven support surface profiles, large "spacing loss", and bad performance.